High frequency CO<sub>2</sub> monitoring of soil and vegetation gas exchange with the atmosphere to assess the local carbon balance of a green infrastructure element

The task of assessing the local carbon balance of green infrastructure elements, which is relevant for the Environmental Social–Governance green agenda, can be successfully solved using modern programmable loggers with NDIR technology for detecting CO2 in the air. The main idea of fully automated continuous monitoring of carbon gas exchange consists in periodic pumping of atmospheric air through closed chambers for soil and vegetation, followed by exposure to assess trends in growth (CO2 emission) or CO2 uptake (photosynthesis) trends using in-chamber CO2 loggers. This know-how was implemented in the Serebryanoborsky experimental forestry of ILAN RAS in Moscow on the example of planting blue spruce (Picea pungens Engelm.) on cultivated loamy sand Cambisol. Budget gas analyzers HT-401/5 (China) with registration every minute were used as CO2 loggers. The monitoring results revealed strong changes in the plant and soil components of C-gas exchange with multiple changes in the local carbon balance from source to sink during the year. Carbon emission losses in the cold period for the soil amount to 8%, and for the plant exceed 17% of the annual flows, without completely stopping even in severe frosts. The share of gross photosynthesis of an evergreen plant exceeds 15% due to periodic winter thaws. Despite a positive annual integral estimate of about 100 gC/(m2 year), the dynamics of the C-balance has a complex oscillatory character with nonlinear reactions of C-flows to temperature, which devalues the widespread estimate with rare measurements of gas fluxes and subsequent temperature extrapolation.